Fuel quality demands and environmental concerns have led to the widespread removal of antiknock additives containing lead, and to the subsequent reformulation of gasoline. Because of the demands of modern internal-combustion engines, refiners have had to modify processes and install new processes to produce gasoline feedstocks that contribute to increasing the “octane,” or autoignition resistance. Premature autoignition causes the “knock” in internal combustion engines. Refiners have used a variety of processes to upgrade the gasoline feedstocks, including higher fluid catalytic cracking (FCC), isomerization of light naphtha, higher severity catalytic reforming, and the use of oxygenated compounds. Some of these processes produce higher octane gasoline feedstocks by increasing the aromatics content of the gasoline at the expense of reducing the content low-octane paraffins. Gasolines generally have aromatics contents of about 30% or more.
Faced with tightening automotive emission standards, refiners are having to supply reformulated gasoline to meet the stricter standards. Requirements for the reformulated gasoline include lower vapor pressure, lower final boiling point, increased oxygenate content, and lower content of olefins and aromatics. Aromatics, in particular benzene and toluene, have been the principal source of increasing the octane of gasoline with the removal of lead compounds, but now the aromatics content may eventually be reduced to less than 25% in major urban areas and to even lower ranges, such as less than 15%, in areas having severe pollution problems.
Alternate formulations for gasolines have been comprising aliphatic-rich compositions in order to maintain the octane ratings, as refiners have worked to reduce the aromatic and olefin content of gasolines. Currently, the processes for increasing the aliphatic content of gasolines include the isomerization of light naphtha, isomerization of paraffins, upgrading of cyclic naphthas, and increased blending of oxygenates. However, oxygenates are also becoming an issue as the use of methyl tertiary-butyl ether (MTBE) is being phased out, and ethanol has become the primary oxygenate for use with gasoline.
New technology, and processes can increase the production of alkylates for gasoline blending to reduce the aromatic content. Adding a complementary unit to process butenes to existing refinery process units provides a convenient upgrade, while improving the economic returns of a refinery with a minimal capital cost, and increases the flexibility of a refinery to shifting product demands.